Process of manufacturing steel.



UNITED STATES PATENT OFFICE.

ANDREWM F. MITCHELL, OF MUNHALL, PENNSYLVANIA.

PROCESS OF MANUFACTURING STEEL.

SPECIFICATION forming part of Letters Patent No. 721,061, dated February 17, 1903 Application filed April 11,1901. erial No. 55,369. (No specimens.)

To all whom it may concern:

Beit known that I, ANDREW F. MITCHELL, a resident of Munhall, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in' Processes for the Man ufactureof Steel; and I do hereby declare the following to be a full, clear, and exact description thereof.

My invention relates to the manufacture of steel, and has for its object to provide a process for improving the quality of articles made therefrom.

The main object of myinvention is to provide means to accomplish this result in steel castings; but it is equally applicable to other articles of steel. For the purpose of accomplishing this result I preferably employ a steel into which nickle, chrome, aluminium, manganese, or an alloy of two or more of these, enters as a constituent.

My process consists in first heating the article to be treated to a temperature above that of recalescence and slowly cooling the article below said temperature, this being repeated until the original granular condition of the steel is changed to a granular condition of such greater fineness as may be desired, and then heating the article to a certain temperature, which varies according to the composition of the steel, but which in all cases lies at or immediately below the temperature of recalescence, instantly stopping the application of heat, all this being accomplished without removal from the furnace in which the first heating was done, and then cooling the article either naturally, by exposure to the air while covered with ashes or other nonconductor of heat while held in a closed receptacle, or by other suitable means.

My process is especially well adapted to the production of steel articlessuch as pinions, rolls, spindles, coupling-boxes, and the like that are required to be very tough.

In case it is desired to secure a hard surface on the article an additional step is necessary. After changing the crystalline condition of the steel into a fibrous one by means of the former treatment I reheat the article to be treated by arapid severe heat applied to the surface of the object or a particular part thereof to a point somewhat above that formerly used and then cool the article in any desired manner, as by water or other cooling liquid. For this purpose I preferably use a steel having a high degree of carbon content. The purpose of this rapid heating being to avoid the exccessive heating of the remainder of the article, it is obvious that if any mentary constituents, principally carbon, in

the ingot and throughout the mass, and the only following heat treatments being for forging or rolling to finished gage, fiberizing, bending or shaping, tempering, and finally rectification of shape after the tempering. My treatment also differs in that it is directly applicable to the casting before subjecting the same to any forming or machining.

My process will be thus seen to consist in heating the steel above the temperature of recalescence one or more times, allowing it to cool below said temperature after each heating, heating it to a temperature immediately below said temperature and again cooling it, and finally, if desired, hardening 0r chilling the exposed or wearing surface or surfaces of the article to the desired depth.

I do not wish to confine myself to the exact form of the process as herein described, but Wish to include all such variants as properly come within the scope of my invention as defined by the claims.

Having thus described my invention, what I claim as new, and desire to protect by Letters Patent, is-

1. The herein-described process for toughening and hardening steel, consisting in subjecting the steel to a heat sufficient to raise the temperature thereof above recalescence, then cooling the steel to a temperature below recalescence Without removal from the heating-furnace, again heating the steel to a temperature immediately below recalescence, and then again cooling the same, substantially as described. I

2. The herein-described process for toughsaid temperature without removal from the furnace, again heating the steel to a temperature near recalescence, and finally treating the steel by heating a portion thereof to a teinperatu re above reoalescence and then cooling the same.

In testimony whereof I, the said ANDREW F. MITCHELL, have hereunto set my hand. :0

ANDREW F. MITCHELL.

Witnesses:

Mrs. J. S. GIBSON, EDWIN B. LYON. 

